The present invention relates to an air bearing with a vacuum preloading function.
Conventionally, many air bearings are used for high-precision measuring equipment such as a coordinate measuring machine and a guiding mechanism of a high-precision machine tool. When compressed air provided from an exterior compressor to an air bearing is supplied to a guide face of a guiding mechanism, an air film is generated between a bearing surface and the guide face of the air bearing. Accordingly, the bearing surface floats from the guide face, and so a guiding mechanism with substantially zero-sliding resistance can be realized.
It is known that the air film has a characteristic that its stiffness varies non-linearly in accordance with a load applied on the air bearing, and the stiffness of the air film is low and unstable in a light-load state. Accordingly, in order to secure the stiffness of the air film between the bearing surface and the guide surface, a technique for controlling the thickness of the air film to be constant is adopted using the vacuum preload method by the suction force due to a negative pressure as shown in, for example, Japanese Unexamined Patent Application Publication No. 2005-037201.
However, piping for connecting the air bearing and the compressor to supply the compressed air and piping for connecting the air bearing and the vacuum pump to obtain the negative pressure are separately required for the vacuum preloading method of Japanese Unexamined Patent Application Publication No. 2005-037201. For this reason, the entire apparatus including the air bearing becomes large and complicated.